Photographic products and processes utilizing 2, 5-dimercapto-1, 3, 4-thiadiazole as an antifoggant



United States Patent 3,330,657 PHOTOGRAPHIC PRODUCTS AND PROCESSES UTILIZING 2,5-DIMERCAPTO-1,3,4-THIADIA- ZOLE AS AN ANTIFOGGANT Peter H. Roth, Watertown, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware N0 Drawing. Filed Oct. 23, 1963, Ser. No. 318,203

4 Claims. (CI. 96-29) The present invention is concerned with photography and, more particularly, with novel photographic products and processes which utilize novel antifoggants and stabilizers.

One object of the present invention is to provide novel antifoggants and stabilizers.

Another object of the present invention is to provide novel antifoggants and stabilizers for silver halide emulsions which do not interfere with the speed or sensitivity of said emulsions.

A further object is to provide novel antifoggants and stabilizers which are useful in photosensitive elements particularly adapted for employment in diffusion transfer processes and especially in dye developer diffusion transfer processes.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

It is well known in the photographic art that light-sensitive silver halide emulsions, due to factors such as encountered during manufacture, storage and/or development, tend to fog. For this reason, it has been generally the practice to employ antifoggants and stabilizers to counteract this effect. Although various materials have been proposed for this purpose, it has been found that the antifoggants, in addition to reducing the fog, have a tendency to adversely affect the sensitivity of the film.

It has now been found that fog, due to conditions encountered during manufacture and storage as Well as in development, may be substantially reduced, without adversely affecting the sensitivity of the emulsion, by using as a stabilizer and/or antifoggant, 2,5-dimercapto-1,3,4- thiadiazole of the formula:

The thiadiazole antifoggant of the present invention is particularly useful in silver and color diffusion transfer processes and, especially in color diffusion transfer processes of the dye developer type, wherein, in addition to reducing fog, said antifoggant has also been found to bring about a substantial increase in the density of the transfer image.

Generally, in diffusion transfer processes an exposed silver halide emulsion is developed and, under the control of the development, an imagewise distribution of imageforming components is formed which is transferred, at least in part, to a superposed image-receiving layer to form the transfer image thereon. In silver diffusion transfer processes, an exposed silver halide emulsion is developed with a silver halide developing agent in the pres ence of a silver halide solvent such, for example, as a thiosulfate or thiocyanate. Almost concurrently with the development of the latent image, the silver halide solvent reacts with the silver halide in unexposed and undeveloped areas to form a soluble, mobile silver complex. At least a portion of the silver complex is transferred to a printreceiving layer where it is precipitated to form the positive image. Suitable examples of such processes are disclosed in patents such as US. Patent No. 2,647,056 to Edwin H. Land.

Generally, in carrying out color difiusion transfer processes, a silver halide emulsion is exposed to create therein a latent image. The latent image is developed and concurrent with and under control of this development, an imagewise distribution of mobile color-providing materials, usually comprising one or more dyes or dye intermediates, is formed. At least a portion of these color-providing materials is transferred to a superposed image-receiving layer to form a colored positive image thereon. As examples of such processes, mention may be made of the processes disclosed and claimed in US. Patent No. 2,983,606, issued May 9, 1961, to Howard G. Rogers, wherein dye developers (i.e., compounds which are both dyes and silver halide developing agents) are the colorproviding materials; the processes claimed and disclosed in U.S. Patent No. 2,647,049, issued July 28, 1953, to Edwin H. Land, wherein color developers are employed to develop the latent image and color couplers are the color-providing materials; and the processes disclosed in US. Patent No. 2,774,668, issued Dec. 18, 1956, to Howard G. Rogers, wherein complete, preformed dyes are used as the color-providing substances.

As pointed out above, the antifoggants of the present invention are especially useful in color diffusion transfer processes employing dye developers, i.e., compounds which are both dyes and silver halide developing agents. Generally, in carrying out such processes, the dye developers are preferably disposed in the photosensitive element in a separate alkali-permeable layer contiguous with the silver halide emulsion layer. After exposure, the photosensitive element is permeated with an alkaline processing solution which solubilizes the dye developer. As a consequence of the development, the dye developer is immobilized in exposed areas. In unexposed and partially exposed areas of the emulsion, the dye developer is unreacted and diffusible and thus provides an imagewise mobile distribution of the dye developer. At least a portion of the imagewise distribution of the dye developer is trans ferred to a superposed image-receiving layer to form the positive image thereon.

Multicolor images may be obtained using color imageforming components such as, for example, the previously-mentioned dye developers, in diffusion transfer processes by several techniques. One such technique contemplates the use of a photosensitive silve halide stratum comprising at least two sets of selectively sensitized minute photosensitive elements arranged in the form of a photosensitive screen. Transfer processes of this type are disclosed in U.S. Patents Nos. 2,968,554 and 2,983,606. Another process for obtaining multicolor transfer images utilizing dye developers employs an integral multilayer photosensitive element, such as is disclosed in copending US. application Ser. No. 565,135, filed Feb. '13, 1956, wherein at least two selectively sensitized photosensitive strata are superposed on :a single support and are processed, simultaneously and without separation, with a single, common image-receiving layer. A suitable arrangement of this type comprises a support carrying a redsensitive silver halide emulsion stratum, a green-sensitive silver hailde emulsion stratum and a blue-sensitive silver halide emulsion stratum, said emulsions having associated therewith, respectively, for example, a cyan dye developer, a magneta dye developer and a yellow dye developer. The

be utilized in the silver halide emulin the form of particles, or it may be employed as a layer behind the appropriate silver halide emulsion strata. Each set of silver halide emulsion and associated dye developer strata may be dye developer may sion layer, for example,

were first stored for seven sed and FIRST SET OF PHOTOSENSITIVE ELEMENTS Antifoggant D ux. of Dunn. of Gamma of Log Toe Sec. 1 Min. in mgs. lg. Positive Positive Positive Speed of Fog Fog Ag. (reflection) Positive (negative) (negative) SECOND SET OF PHOTOSENSITIVE ELEMENTS (AGED) separated from other sets by suitable interlayers, for example, by a layer of gelatin or polyvinyl alcohol.

Generally, the amount of thiadiazole antifoggant employed may be varied depending on the fogging characteristics of the silver halide emulsion which is to be stabilized. Preferably less than 3 mgs. of the thiadiazole antifoggant and more particularly between about 0.1 to about 3 mgs. of the thiadiazole antifoggant are used per gram of silver. Especially effective results have been obtained using about 0.5 to about 1.5 mgs. of said antifoggant per gram of silver.

The thiadiazole antifoggant of the present invention may be effectively located in one or more silver halide emulsion layers and/or in adjacent layers of a film unit and/ or in the processing solutions. Particularly effective results have been obtained by incorporating the antifoggant directly in the emulsion layers.

The following nonlimiting example illustrates the processes and products of the present invention.

Example Film units were prepared by coating gelatin-subcoated film bases with 4% gelating coating solutions comprising sufficient 1,4-bis- (a-methyl-;9-hydroquinonylethylamino) 5,8-dihydroxyanthraquinone (a cyan dye developer disclosed in the copending application of Blout et al., Ser. No. 233,461, filed Oct. 26, 1962) dispersed therein to give a coverage of about 100 to about 110 mgs. per square foot. After these coatings had dried, silver iodobromide emulsion coatings comprising about 270 to 300 mgs. of silver per square foot and respectively 0.0 (control), 0.5 and 1.0 mg. of 2,5-dimercapto-1,3,4-thiadiazole (obtainable from the Fairmont Chemical Co., New York, NY.) per gram of silver were applied. One set of the photosensitive elements were exposed and processed by spreading an aqueous liquid processing composition comprising:

Water cc 100 Sodium hydroxide grams 5.0 Hydroxyethyl cellulose do 4.03 Benzotriazole do 2.3 N-benzyl-a-picolinium bromide do 2.3 Sodium thiosulfate 1.15

between said photosensitive element and an image-receiving element comprising a sheet of cellulose acetate subcoated baryta paper having coated thereon a mixture of polyvinyl alcohol and poly-4-vinylpyridine, as said elements were brought into superposed relationship. After an imbibition period of 1 minute the image-receiving element was separated to reveal a monochromatic reversed cyan dye image of the photographed subject.

Although the antifoggant of this invention was illustrated in diffusion transfer processes, it should be understood that it is effective in reducing fog is conventional photographic products and processes.

Although, as illustrated in example, the antifoggant is directly incorporated in the silver halide emulsion itself, it will be recognized that it can be effectively incorporated, in part or in whole, in the processing composition and/or other layers of the filament unit, for example, in a permeable layer adjacent the silver halide emulsion. In general, the most efficacious method has been determined to be that of directly disposing it in the silver halide emulsion. For example, the thiadiazole antifoggant may be advantageously incorporated in the silver halide emulsion during the ripening or sensitivity increasing stage of the emulsion manufacturing process or as a coating final just prior to coating the emulsion on a suitable support.

It will be understood that silver halides of varying halide concentrations may be advantageously employed and that the silver halide emulsions employed may be chemically sensitized by any of the accepted procedures. For example, the emulsions may be chemically sensitized with sulfur compounds such as sodium thiosulfate or thiourea; with reducing substances such as stannous chloride; with salts of noble metals such as gold, rhodium and platinum; with amines and polyamines; with quaternary ammonium compounds; and with polyethylene glycols and derivatives of same.

The emulsions may also be optically sensitized with cyanine and merocyanine dyes as described in US. Patents Nos. 1,846,301, 1,846,302, 1,942,854, 1,990,507, 2,112,140, 2,165,338, 2,493,747, 2,493,748, 2,503,776, 2,519,001, 2,666,761, 2,734,900, 2,739,964, etc.; and where desired, suitable restrainers, accelerators, preservatives, coating aids, and/ or additional stabilizers may be included in the composition of the emulsion.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic product which comprises a plurality of layers including a support, a silver halide gelatin emulsion located in a layer on said support, a dye developer in one of said layers on the same side of said support as the silver halide emulsion layer, said silver halide gelatin emulsion having therein 2,5-dimercapto- 1,3,4-thiadiazole in an amount sufficient to act as an antifoggant.

2. In a process for forming diffusion transfer images in color which comprises the steps of developing an exposed silver halide emulsion in the presence of a dye, said dye being a silver halide developing agent, immobilizing said dye in the exposed areas as a resultant of development, forming thereby an imagewise distribution of mobile dye in unexposed areas, and transferring, by imbibition, at least a portion of said imagewise distribution of mobile dye to a superposed image-receiving layer to provide thereon a positive dye image, the improvement which comprises conducting said process in the presence of a 2,5-dimercapto-1,3,4-thiadiazole antifoggant.

3. A process as defined in claim 2 wherein about 0.1 to about 3 milligrams of said antifoggant are present per gram of silver.

4. A process as defined in claim 2 wherein about 0.5 to about 1.5 milligrams of said antifoggant are present per gram of silver.

References Cited UNITED STATES PATENTS 2,573,027 10/1951 Kendall et al. 96-109 2,983,606 6/1961 Rogers 96-29 3,148,987 9/1964 Willems 9652 NORMAN G. TORCHIN, Primary Examiner. J. TRAVIS BROWN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,330 ,657 July 11 1967 Peter H. Roth It is hereby certified that error appears in the above numbered pat- Patent should read as ent requiring correction and that the said Letters corrected below.

Column 3, line 45, for "gelating" read gelatin line 66 for "Sodium thiosulfate l. 15" read Sodium thiosulfate a v do --1 1S column 4 line 25 for "is" second occurrence read in line 27 after "in" insert the column 5 line 3 for "resultant" read result column 6, line 8 for "6/1961" read 5/1961 Signed and sealed this 23rd day of July 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

2. IN A PROCESS FOR FORMING DIFFUSION TRANSFER IMAGES IN COLOR WHICH COMPRISES THE STEPS OF DEVELOPING AN EXPOSED SILVER HALIDE EMULSION IN THE PRESENCE OF A DYE, SAID DYE BEING A SILVER HALIDE DEVELOPING AGENT, IMMOBILIZING SAID DYE IN THE EXPOSED AREAS AS A RESULTANT OF DEVELOPMENT, FORMING THEREBY AN IMAGEWISE DISTRIBUTION OF MOBILE DYE IN UNEXPOSED AREAS, AND TRANSFERRING, BY IMBIBITION, AT LEAST A PORTION OF SAID IMAGEWISE DISTRIBUTION OF MOBILE DYE TO A SUPERPOSED IMAGE-RECEIVING LAYER TO PROVIDE THEREON A POSITIVE DYE IMAGE, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID PROCESS IN THE PRESENCE OF A 2,5-DIMERCAPTO-1,3,4-THIADIAZOLE ANTIFOGGANT. 